70 



XATCRAL HISTORY OF ARTHROPODS. 



Fig. S9. — Leptochtl'ta aUiicola. enlarged twenty tinies. 



" sow-buo-s," live on the laml. The IsopoJa are usually divided into two groups, 

 named, respectively, Ambulatoria and Xatatoria, according to their Avalking or swim- 

 ming habits, with which are correhited many anatomical features. We will here, how- 

 ever, omit these two larger divisions, and proceed at once to the discussion of the 

 families. 



The lirst of these families, tlie Taxalli-E. is of doubtfid position, but, according to 

 Fritz Midler (whose opinions are seconded bv other authorities) they probably repre- 

 sent an ancestral type of Isopoda. 



They differ from all other Isop)oda 

 in having the respiratory organs be- 

 neath the head and first thoracic seg- 

 ment, the eyes, when present, upon 

 jointed stalks, while the abdominal 

 appendages have no respiratory func- 

 tion, and the first pair of ambulatory feet are chelate. In their embryology the 

 Tanaidie are said to present points of resemblance to Asdliis^ JLi/gia, and Cuma. 

 But two genera, Tanais and I^eptochelia, are rejiresented, 

 so far as is known, upon our shores. 



In the GxATHiiD.E we find a type more allied to the 

 normal isopod. The thorax appareutlv consists of five 

 segments, and only five pairs of limli< possess the normal 

 form. In the typical genus Gnotlila ('P raniza awA Aitctiig 

 of authors) there is a great difference between the males 

 and females, so great, in fact, that different sub-families 

 have been erected for the two sexes of the same species. 

 The larvse are more nearly like the normal isoj>od than are 

 the adult. A single species, (t. '•iriiai^ is found on the 

 New England coast. 



Passing the Anthi rid-E. a small group of slender 

 forms, the next families to be noticed are the Cv.moth- 

 EEID.E, ^Egid_e, and Cirolaxid^, which embrace most 

 of the jjarasitie forms of this order. Yet the parasitic 



habits have not produced such a profound effect upon the struc- 

 ture as among the root-barnacles and the Siphonantia, alreadv de- 

 scribed. From their habits the teiau "fish lice" is 

 eminently appropriate for them, as thev live at- 

 tached to the integument or within the mouth of 

 fishes. Usually these three families are considered 

 as one, under the name ^Egid.T. They all aaree in 

 having all of the segments behind the head dis- / 

 tinct, and in the lack of an operculum closing- in ' 

 the respiratorv eavitv. 



Among the more Lnterestint; forms belonging 

 to this family may be mentioned ^iV/rt^xso/vy, the 

 "salve-bug" of the fishermen, which is frequently 

 found attached by its sharp claws to the cod and halibut, and Ci/mothoa 

 priRgu.ito.tor. which occurs attached to the roof of the mouth of the 

 menhaden. Mr. .1. F. Bullar has shown that in certain genera ( Cguio- J;.',™f;kKe.^ug 



f'O. — Gnathia, male. 



Fig. 91. — Gnathia, 

 female. 



